In recent years, a variety of digital instruments have been developed as digital signal processing techniques are improved. Small-sized digital video recorders for recording digital video signals in the form of compressed codes have been realized lately. Among various methods that have been proposed for the compression coding of digital video signals, two-dimensional discrete cosine transform (DCT) coding, which is one of the methods for frequency conversion of digital video signals in the unit of a block, has become the mainstream as used in JPEG and MPEG. In this method, digital video signals are divided into a plurality of coding blocks and discrete cosine transform is performed for each coding block, and further the resulting coefficient data are subjected to variable-length coding for each block, to compress data.
However, in such a recording and reproducing apparatus using compression coding, if an error has occurred to data during the recording or reproducing process, variable-length codes in a certain range subsequent to the error occurrence point could not be decoded. Also, even if the variable-length decoding is refreshed by detecting a break in the variable-length code by means of refresh codes or the like, the variable-length codes themselves over a range from the occurrence of an error to the refreshing could not be decoded. In such a case, the image would drop out in the unit of the block on the reproduction screen, and the dropping out would succeed over several blocks.
In order to solve this problem in the compression coding, in the recording and reproducing apparatus with image coding described in Japanese Patent Laid-Open Publication 7-298194/1995 by the present inventors, errors are corrected by using coefficient data of neighboring coding blocks having high spatial correlation. In this error correction, for recording, coefficient data within one coding block are mixed with coefficient data of a boundary portion within a neighboring coding block and subjected to shuffling. In the shuffling, it has also been proposed to divide neighboring coding blocks so that their boundary portion is shared therebetween. Then, the discrete cosine transform is performed with respect to coding blocks constituting the same region on the screen, the resulting coefficient data are classified into groups, and the groups are recorded in separate regions on the recording medium. In this apparatus, even if an error occurs during recording or reproducing process, there will never occur any collective disappearance of associated coefficient data. Further, even if coefficient data has disappeared upon occurrence of an error, correct data can be restored more accurately by using the correlation of coefficient data. Therefore, the stability of recording and reproducing operations can be greatly enhanced without causing the image to disappear in blocks.
However, even in this recording and reproducing apparatus with image coding, if a plurality of errors of coefficient data have occurred within the same coding block, correct restoration by error correction cannot be done. It is desirable that an error can be corrected so that image is not dropped out in such a situation as mentioned above.